Hemiascomycetous yeast splice motifs are well conserved and are typically less degenerate than in most eukaryotes, including fungi [Lorkovic et al., 2000; Wood et al., 2002].
Thus, a set of 17 distinct 5' motifs have been detected in the hemiascomycetous yeast species compared to 100 in S. pombe [see ftp://ftp.sanger.ac.uk/pub/yeast/pombe/Intron_Data/] . Only three of these 17 motifs are preferential 5' motifs: GTATGT, GTAAGT or GTGAGT, depending on the phylogenetic position of the yeast species [Bon et al., 2003].
Similarly, TACTAAC, is the most common branch motif [Spingola et al., 1999, RNA, 5, 221-234; Bon et al., 2003]. In contrast, only shorter and more degenerate motifs are found at this location in human and S. pombe, in which YTRAY is proposed to be the consensual branch motif [Zhang & Marr, 1994].
Together with these preferential motifs, some divergent 5' and branch motifs also exist but in a less greater frequency [Bon et al., 2003].
The 3' splice motifs appear much more conserved with only three possible motifs in eukaryotes: TAG, CAG being the most common and AAG being more rare [Rymond & Rosbash, 1992, Cold Spring Harbor Laboratory Press, 2, 143-192; Brown, 1986, NAR, 14, 9549-9559; Zhang et al., 1994, Nature, 372, 809-812]. YAG was the most common 3' motif in hemiascomycetes [Bon et al., 2003].